Heating apparatus



Jan. 23, 1940.

W. M. HEPBURN HEATING APPARATUS Filed Nov. 11, 1957 ZSmaentor (IttornegPatented Jan...23, 1940 HEATING APPARATUS William M. Hepburn, OttawaHills, Ohio, assignor to Surface Combustion Corporation, Toledo, Ohio, acorporation New York Application November 11, 1937, Serial No. 174,087

4 Claims.

This invention relates to heating apparatus comprising a fuel-firedradiator tube for producing radiant heat in a furnace chamber and anexhaust fan for the double purpose of withdrawing gases of combustionfrom the tube and for drawing combustion-supporting air into the intakeend of the tube: and the object of the invention is to increase theutility of such apparatus by the improvements hereinafter described.

In the drawing wherein the preferred form of the invention is shown:

Fig. 1 is a side elevation of the improved heating apparatus with partsin section;

Fig. 2 is a sectional view on line 2-2 of Fig. 1;

Fig. 3 is a sectional view on line 3--3 of Fig. l, and

Fig. 4 is a sectional view of the burner associated with the radiatortube.

Referring to Fig. 1, ll indicates a wall of a furnace chamber wherein ispostioned a fuelfired radiator tube l2 which, for convenience ofillustration, is shown as of the hairpin type with its free endsprojecting out of said chamber which leads from a chamber l4 to whichfuel gas is supplied by a gas pipe I, it being noted that the tube llextends a substantial distance into the radiator tube i2 beyond themouth l2 of the latter. fuel flowing from the fuel tube II enters theradiator tube l2 at its mouth l2, the air being drawn into said mouth bya suction fan ll coupled to the exhaust end of the radiator tube l2 bymeans including an exhaust pipe II. In order to insure ignition of thefuel gas discharg from the fuel tube It, a stream of premixed air andgas is caused to burn around the discharge end of said tube, saidmixture being delivered to said end by means including a pipe I! towhich the mixture is delivered by a supply pipe-20, it being noted thatthe pipe I! surrounds the fuel tube in spaced relation and terminatesshort of the discharge end of the latter. To prevent said mixture frombackflring there is provided between the two tubes a ring 2| providedwith restricted discharge passages. The burner A thus briefly describedforms, per so, no part of the present invention.

Positioned in the radiator tube l2 in front of the fuel tube I3 is a.sleeve 24 which is held spaced from the'walls of the radiator tube byspacer fingers 25, thus providing a flow space 24 between The air forsupporting combustion of the the sleeve 24 and the radiator tube. Thepurpose of the sleeve 24 will be presently explained.

The exhaust pipe I8 is internally and externally provided with heatconducting fins 2'! and 28 respectively, and is surrounded by a casing29 into whose upper end fuel gas is discharged by a supply i5 and fromwhose lower end the fuel gas flows into the pipe I5 leading to theburner A, it being understood that by heat exchange between the fuel gasand the exhaust gases, the latter become cooled and the fuel gas becomesheated.

Let us now briefly consider some of the advantages resulting fromeffecting heat exchange between the outgoing exhaust gas and theincoming fuel gas.

It is a characteristic of fan performance that the static suction isdirectly proportional to the density and therefore inverselyproportional to the absolute temperature of the gases entering the fan.This is expressed by the equations S=KD and where S=static suction;D=density of the. gas;

T=absolute temperature of the gas, and K=a constant. Thus with everytemperature change of gases entering the fan, the static suction of thefan will always change. Likewise when the static suction of the fanchanges the quantity of the gases by weight handled by the fan will alsochange.

Now let us consider what takes place when a fan is utilized for the dualpurpose of expelling combustion gases from an internally fired radiatortube and for drawing combustion supporting air into the tube. In thefirst place let us assume that fuel gas is being supplied to .the intakeend of the tube at a constant rate by weight and that the static suctionof the fan when the combustion gases at the fan are, at'somepredetermined temperature, say 1000 F., is just enough to cause therequired amount of combustion supporting air to enter the radiator. Asthe temperature of the exhaust gases increases the rate of air by weightdrawn into the tube by the fan decreases with the result that the amountof oxygen delivered to the fuel for supporting its combustion isdecreased. This is the same thing as saying that the air to gas ratiodecreases as the static suction of the fan decreases or as thetemperature of the exhaust gases pulled out of the tube by the fanincreases.

In the operation of a furnace wherein the temperature variation is smallafter the normal operating temperature has 'been reached and thereforewhere the exhaust gas temperatures are substantially constant, thevariation in air to fuel weight ratio is exceedingly slight and theproblem of controhing this ratio is not necessarily of great importance.However, the temperature of the exhaust gases varies considerably duringthe warming-up period, but as this period is relatively short, theinefficiency due to the changing air to fuel weight ratio is negligible.

However, in furnaces wherein the operating temperature variation isappreciable, such as furnaces which are used for two or more heatingoperations requiring more than one operating temperature, themaintenance of proper air to fuel weight ratio without readjusting theburner equipment for each temperature change is of considerableimportance.

By the present invention the air to fuel weighttion of the exhaust fan.Moreover since the de-,

gree to which the fuel gas is heated and therefore expanded is directlyproportional to the temperature of the exhaust gases, it will beappreciated that the degree of expansion of the fuel gas isautomatically controlled.

The conduit or sleeve 24 serves to provide a constricted combustion'zone in which the fuel discharged therein will only partially-burn dueto the insufficiency of air drawn into the sleeve, the major portion ofthe air for combustion being drawn around the sleeve in the passage 26.As the unburned fuel leaves the sleeve 24, it slowly diffuses with theair fiowing through the annular passage 26, thereby lengthening the zoneof combustion. This results in an elongated and more uniform flame whichprovides improved temperature distribution throughout the radiator tube.

From the foregoing it will be seen that the present inventionsubstantially increases the heating efi'iciency of heating apparatuscomprising a fuel fired radiator tube, also permits use of lean producergases and blast furnace gas for higher temperature application thancould normally be attained.

What I claim is:

1. In combination, a fuel-fired radiator tube, a burner firing into theintake end of said tube,

a fan at the discharge end of said tube for producing a suction,therethrough, and means for maintaining a substantially constant air tofuel weight ratio at the intake end of said tube comprising means forcooling the exhaust gases entering said fan whereby the static suctionof said fan will remain substantially constant and simultaneouslyproportionally heating the fuel being supplied to said burner.

2. In combination, a fuel-fired radiator tube, a burner firing into theintake end of said tube; a fan at the discharge end of said tube forwithdrawing gases of combustion therefrom and for inducing a flow of airinto the intake end thereof, and means for cooling the exhaust gasesbefore they enter said fan comprising means for heating the fuel beforethe same is discharged into the tube.

3. In combination, a fuel-fired radiator tube, a

"burner firing into the intake end of said tube, a

fan at the discharge end of said tube for producing a suctiontherethrough, and means for maintaining a substantially constant air tofuel weight ratio at the intake end of said tube comprising means forheating the fuel proportional to the temperature of the gases ofcombustion discharged from said tube.

4. In combination, a furnace chamber, an internally fired tube withinsaid chamber for producing radiant heat therein, a suction fan forwithdrawing gases of combustion from said tube, means outside of saidchamber for absorbing heat from said gases before they reach said fan,means for transferring the absorbed heat to a gaseous medium, and meansfor transferring said medium to the intake end of said tube. 1

WILLIAM M. HEPBURN.

